1. Field of the Invention
The present invention relates to a multi-speed automatic transmission, adapted for a motor vehicle, which has a planetary gear sets and is arranged in a lateral direction of its vehicle body.
2. Description of the Related Art
Recently, automatic transmissions mounted on motor vehicles require more forward speeds, for example more than six forward speeds, in order to improve fuel consumption, exhaust emission purification, and accelerating performance. Such a conventional multi-speed automatic transmission for a motor vehicle is disclosed in Japanese patent laid-open publication No. (Tokkaihei) 04-219553. This conventional multi-speed automatic transmission has two gear sets, one of which is a Ravigneaux type planetary gear set, or three gear sets associated with five friction elements to provide forward 6-speeds. These gear sets and friction elements are arranged in series in an axial direction of the transmission, which requires space longer in the axial direction and causes great difficulties for its installation on a motor vehicle such as a front-engine front-drive (FF) vehicle and a rear-engine rear-drive (RR) vehicle, in which the transmission is arranged in a lateral direction of a vehicle body.
In order to avoid such a disadvantage, another conventional multi-speed automatic transmission has been proposed, and disclosed in Japanese patent laid-open publication No. 2005-180665. This conventional transmission has two planetary gear sets and five to six friction elements, the planetary gear sets and the friction elements being separated into two groups to be arranged on two parallel shafts.
This conventional multi-speed automatic transmission, however, can not avoid arrangement of four friction elements, consisting of two clutches and two brakes, from being arranged in series on an axis of one of the planetary gear set, although its axial length can be shorten in comparison with the former conventional automatic transmission. Especially, one brake can not avoid being arranged at an outer side of a chain connecting a first planetary gear set and a second planetary gear set. This requires further improvement in decreasing its axial directional length in order to install the automatic transmission on a smaller vehicle.
It is, therefore, an object of the present invention to provide a multi-speed automatic transmission adapted for a motor vehicle which overcomes the foregoing drawbacks and can decrease an axial length of the automatic transmission for easily installing it on a smaller vehicle, obtaining appropriate transmission gear ratios corresponding to more than six forward speeds.